Field of the Invention
Embodiments of the invention relate to a method for producing a thermal barrier film composed of a polyvinyl chloride resin composition. More specifically, embodiments of the invention relate to a method for producing a thermal barrier film composed of a polyvinyl chloride resin composition, the film having high visible light transmittance while showing thermal barrier properties by efficiently blocking near-infrared rays of sunlight during daytime, thus being capable of suppressing temperature increase inside agricultural and horticultural facilities such as agricultural and horticultural greenhouses, and having low heat transmission at night, thus being capable of reducing heat dissipation from the agricultural and horticultural facilities.
Description of the Related Art
Conventionally, agricultural and horticultural facilities such as agricultural and horticultural greenhouses that use resin films such as polyvinyl chloride resin films, polyethylene resin films, and fluorine-containing polymer resin films as roofing materials or wall materials have been utilized in farming agricultural and horticultural crops. Such agricultural and horticultural facilities are used for purposes such as heat retention, wind protection, rain protection, and snow protection during winter, and are used for purposes such as wind protection, rain protection, insect protection, and insect pollination during summer. However, in the case of agricultural and horticultural crops such as strawberry and lettuce, the growth of which is disturbed by high temperatures inside the agricultural and horticultural facilities due to exposure to strong sunlight, the agricultural and horticultural facilities that use such resin films mentioned above as roofing materials or wall materials have a disadvantage of the need for countermeasures such as temperature adjustment by covering them with cheesecloths or shading nets or partially opening the roof or the wall. Therefore, there has been a demand for agricultural and horticultural facilities that do not require such complicated countermeasures also in the case of agricultural and horticultural crops such as strawberry and lettuce. Further, it is desired to show heat retention properties at night while expressing thermal barrier properties during daytime, in the season when the diurnal range of temperature is large.
Therefore, as techniques for such an application, films that transmit visible light, while showing thermal barrier properties by blocking near-infrared rays have been proposed as materials for agricultural and horticultural facilities according to the conventional art. However, it is difficult to well disperse a thermal barrier material in a resin that is a polymer material. Conventional art, for example, JP 2002-369629 A, discloses an agricultural and horticultural heat insulating material including a heat insulating layer composed of a resin substrate in which a heat insulating filler selected from lanthanum hexaboride and antimony-doped tin oxide is dispersed. Further, conventional art, for example, JP 2002-369629 A, discloses a method for producing a heat insulating material including simultaneously mixing a heat insulating filler and a resin material. However, in the method disclosed in JP 2002-369629 A, dispersion of the thermal barrier material is insufficient. Meanwhile, conventional art also discloses resin films including a thermoplastic resin film containing titanium oxide (see, for example, JP 2006-314218 A and JP 2007-222061 A). However, the techniques of these conventional art references exhibit a low shielding factor from near-infrared rays and have insufficient thermal barrier properties.